Borneo Tree Hole Frog

Metaphynella sundana, or the Borneo tree-hole frog, is a member of the microhylid family. It is a small, stocky bodied frog ranging from 19 - 22.5 mm snout-vent length with short limbs. The head of M. sundana is as wide as long and the nose is pointed and longer than the diameter of the eye. The interorbital distance is 1.6 - 2.0 times as wide as the upper eyelid. The tympanum is hidden by a curved supratympanic fold extending from the eye to the axilla. The toes of M. sundana have slightly enlarged tubercles. The fourth toe has only two tubercles. Metaphrynella sundana lacks an outer metatarsal tubercle, and possesses only a small inner metatarsal tubercle, which is oval in shape. The feet have extensive webbing that extends beyond the basal tubercles and leaves only the distal phalanx free of webbing on all but the fourth toe, which has 2 or 3 web-free phalanges. The first finger is shorter than the second (Inger 1966) and the fifth finger is longer than the third (Matsui et al. 1996). The toe pads of M. sundana are truncate and are adhesive (Matsui et al. 1996). Males lack nuptial pads and possess vocal sacs with slit-like openings on the sides of the floor of the mouth. Its skin is tubercular, with the tubercles on its sides being larger (Inger 1966). Coloration ranges from light to dark brown, with darker blotches and patterning dorsally. Some specimens have dark crossbars on the dorsal side of the limbs. Individuals may be ventrally solid colored or splotched, with white or dark spots in some (Inger 1966). In alcohol, M. sundana has grey or brown dorsal coloration with dark irregular markings. Ventrally the frog has dark mottling and a solid black or grey with black spotted throat. Dorsal limb coloration may show crossbars (Inger 1966).Metaphrynella is included in the subfamily Microhylinae with other taxa such as Kaloula and Microhyla (Inger 1966; Matsui et al. 1996).

Metaphrynella sundana is a terrestrial frog endemic to the rainforests of Borneo. It is usually found at 200 m in elevation and prefers flat, low-lying areas (Inger 1966; Lardner and Lakim 2004).

Males call from pools of water that collects in tree holes 1 - 5 m above the ground. They are territorial, and only one male occupies a single tree hole. Males are able to determine the resonance properties of the tree hole they are calling from and adjust their calls to maximize the amplitude of their call. They attract mates with a short, tonal pulse. The males can be heard up to 50 m away. Females prefer calls that are in the lower range of frequencies (Clark 2002; Lardner and Lakim 2004). During the non-seasonal breeding period, females lay their eggs, 1 mm in size (Inger 1966), in the tree hole. These hatch into tadpoles, which develop within the tree hole (Lardner and Lakim 2002 and 2004).

While Metaphrynella sundana is listed as ‘Least Concern’, it is threatened by deforestation of rainforest habitat. In general, the species is widely distributed and assumed to have a large population size. (Inger 2004).

Metaphrynella sundana (Borneo treefrog or Bornean tree hole frog) is a species of frog in the family Microhylidae. It is endemic to Borneo and found in Brunei, Indonesia, and Malaysia.